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Sticky epoxy...Help!

honza992

honza992

Archdale Acoustic Bass
Supporting Member
Commercial Seller
Jan 25, 2006
438
780
Pietrasanta, Italy
#1
Ok, I use epoxy for lots of joints. I use West Systems, I measure accurately using syringes. This time I'm using it to grain fill a walnut-veneered body. The veneer was glued on with WS epoxy. Once sanded I sealed the grain with a couple of costs of hand mixed shellac. Not new, but no more than 3 months old. Last week I grain filled in Friday. On Monday it was hard, but tacky. This has never happened to me before with WS, and I use it a lot. I wiped off what I could with alcohol and sanded back to wood. I reapplied shellac then grain filled again. This morning? Tacky.....arghhhhh what is going on?

The first time I thought maybe I had a brain freeze and either I measured it out wrong or didn't stir enough. So this time I was extra careful. I waited overnight after applying the shellac before doing grain fill.

I know the epoxy itself is good because I've used it for several joints, no problem, it's dried hard with no stickiness. And it's dried hard in the mixing pot.

I've mixed up some fresh shellac from newly bought flakes that I'll use for my next attempt, that's the only thing I can think it could be. Even though I'm sure it's not more than a few months old.

Anyone else have any good ideas? @Bruce Johnson I know you use WS a lot. Ever come across tackiness that never disappears?

Edit: I'm using 105 and 206 slow, both newish. Temperature in shop is not below 60F at the moment.
 
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#5
MPU said:
A thin layer of epoxy dries tacky very easily. Sand the grain filling level and you're done. Don't worry about the amine blush that's causing the stickiness.
You can remove the amine blush with water. I've used Scotchpad with warm soapy water when I made composite basses to remove amine blush.
Click to expand...
Thanks MPU. Would you expect anime blush to be heavily tacky rather than just a bit waxy in feel? This is sticky but not gooey. I can easily leave fingermarks in it...
 
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#7
My concern was that alcohol remaining in the shellac could have interfered with the epoxy. It doesn't take much to contaminate a thin layer of epoxy, since it's such a small volume. I agree that heat may work. My next step would be to put the piece in a big box or a closet with a space heater and try to get it up nice and warm for a day and see what happens.
 
#9
BurnOut said:
I use epoxy quite a bit. Sometimes it hardens right up, other times it takes a day or two to harden up. Usually when it's going slow the epoxy was older. If it's something I want instant good results I'll buy some fresh new stuff for the job at hand.
Click to expand...
This^^^^
Epoxy, like any other glue, has a shelf life. I rotate new epoxy into use every 4 to 6 months.
 
#10
When I spread epoxy across a large surface thinly, it typically dries as you describe above - sticky and tacky due to the amine blush. It sands/scrapes right off and has not been a problem for me before.

Heat is also a factor - I would think around 15C (60F) would close to double the expected time for it to fully cure. Whenever I use epoxy, I always crank the heat while it cures - it seems to help a lot. I let it sit around 25+ C (80F) while its curing. Alternatively, one can use a cold cure epoxy formulated for use in colder temps (we use that a lot up here in the boat-building industry during shoulder seasons and winter repairs).

At any rate, the tackiness you've described does not seem to be outside the range of "normal" in my experience. Then again, some people have used much more, and wider varieties, for longer than I have (lookin' at you @Bruce Johnson :D )...
 
#11
Either something needs more time to cure, or it's been around too long. Fresh supplies, left to cure for longer than the can says (2 to 3 times is what I work with) is almost always a good fix for finish not curing issues.
 
#12
honza992 said:
I've mixed up some fresh shellac from newly bought flakes that I'll use for my next attempt, that's the only thing I can think it could be. Even though I'm sure it's not more than a few months old.
Click to expand...

I suspect the shellac is the culprit, given that the epoxy you've got in the mixing pot is hard. And shellac that is a "few months old" is too old. I buy very small batches of flakes and, because I only do a couple instruments per year, do fresh batches of shellac every time.
 
#13
honza992 said:
Ok, I use epoxy for lots of joints. I use West Systems, I measure accurately using syringes. This time I'm using it to grain fill a walnut-veneered body. The veneer was glued on with WS epoxy. Once sanded I sealed the grain with a couple of costs of hand mixed shellac. Not new, but no more than 3 months old. Last week I grain filled in Friday. On Monday it was hard, but tacky. This has never happened to me before with WS, and I use it a lot. I wiped off what I could with alcohol and sanded back to wood. I reapplied shellac then grain filled again. This morning? Tacky.....arghhhhh what is going on?

The first time I thought maybe I had a brain freeze and either I measured it out wrong or didn't stir enough. So this time I was extra careful. I waited overnight after applying the shellac before doing grain fill.

I know the epoxy itself is good because I've used it for several joints, no problem, it's dried hard with no stickiness. And it's dried hard in the mixing pot.

I've mixed up some fresh shellac from newly bought flakes that I'll use for my next attempt, that's the only thing I can think it could be. Even though I'm sure it's not more than a few months old.

Anyone else have any good ideas? @Bruce Johnson I know you use WS a lot. Ever come across tackiness that never disappears?

Edit: I'm using 105 and 206 slow, both newish. Temperature in shop is not below 60F at the moment.
Click to expand...



For the next time..........

Mix up some as a sample and apply it to a scrap piece of wood, before using. Duplicate the final work, dount leave it in a half dollar puddle after mixing.

If I had to guess, either its reacting with the shellac, have you used that combo before?

Or possibly you mixed up a small amount that wasn't thouroughly mixed?

West Systems are good people, not my flavor for epoxies as they are ridiculously expensive, but they do maintain good records and you could check on the lot numbers of the ingredients.
 
#14
I really don't expect this is due to old product. I've used West System epoxies that were 8 or 9 years old without any issues. Their website claims a useful life of "many years:"

Invalid Link Removed

As it gets old it tends to discolor and get a little thicker, but I've never had curing issues associated with age.
 
#15
I'm sure it's not the epoxy. It was probably 2 weeks old, and I did two joints with it on the same day, no problem....and it's now happened twice, and the second time I was really careful about ratio and mixing (as I always am)

dwizum said:
I really don't expect this is due to old product. I've used West System epoxies that were 8 or 9 years old without any issues. Their website claims a useful life of "many years:"

Invalid Link Removed

As it gets old it tends to discolor and get a little thicker, but I've never had curing issues associated with age.
Click to expand...
 
#16
MPU said:
A thin layer of epoxy dries tacky very easily. Sand the grain filling level and you're done. Don't worry about the amine blush that's causing the stickiness.
You can remove the amine blush with water. I've used Scotchpad with warm soapy water when I made composite basses to remove amine blush.
Click to expand...

I don't generally use epoxies, so "Amine blush" was a new term for me. Thanks for bringing it up, as it fulfilled my daily requirement for "Every day you learn something new".

Invalid Link Removed
 
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#18
Have you thoroughly checked everything else involved with the applications? Maybe some contaminant on the sanding materials, brush, or rag... (And I'm not suggesting you're not working with clean tools) What about the alcohol for the shellac?
 
#19
Sorry I'm late to the discussion....I've been preoccupied with power outages and other craziness....

Maybe I'm confused here, but it doesn't sound like the West Systems epoxy is the problem. It sounds like the West Systems may be interfering with the shellac, preventing the shellac from drying.

My overall question is why are you using the Shellac? The West Systems epoxy will fully seal up and permanently fill the grain by itself. The West Systems should be applied directly to the bare wood, for maximum bonding strength. Applying it over another finish like shellac seems like a bad idea.
 
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#20
Bruce Johnson said:
Sorry I'm late to the discussion....I've been preoccupied with power outages and other craziness....

Maybe I'm confused here, but it doesn't sound like the West Systems epoxy is the problem. It sounds like the West Systems may be interfering with the shellac, preventing the shellac from drying.

My overall question is why are you using the Shellac? The West Systems epoxy will fully seal up and permanently fill the grain by itself. The West Systems should be applied directly to the bare wood, for maximum bonding strength. Applying it over another finish like shellac seems like a bad idea.
Click to expand...

Thanks Bruce, for your input, really appreciated.

I used shellac mostly just to add some colour contrast in the grain - the WS is newly opened so almost completely clear. Also, though, I've previously tried using black epoxy as a grain fill and found that it stained the fields between the grain and it made sanding back really hard. I thought a seal coat would allow the epoxy to go into the grain, but still allow easy sanding all the way back to the wood. I'm not sure if that makes sense?

I take it from your post that you think it's unlikely to be anime blush?

Edit: I waited overnight between applying two light coats of shellac and applying the epoxy. The workshop is pretty warm. I thought shellac was pretty quick drying.....does that sound insufficient?
 

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